JP2006003242A - Measuring method and device using pulse frequency signal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure a small measured value in a system for measuring a plurality of pulse periods (times) and heightening measurement accuracy by taking the average therefrom. <P>SOLUTION: A measured value signal converted into a pulse frequency signal is received, and a pulse frequency is operated from an average period of the prescribed number of sampling pulses, converted into an analog output, and displayed on a display. This device is equipped with a sampling upper-limit time determination part and an input frequency operation part. When the prescribed sampling number A can be measured within a sampling upper-limit time At, the input frequency operation part measures the total time t[sec] of the prescribed sampling number A and determines A/t[Hz] as an input frequency measurement result. When the prescribed sampling number A cannot be measured within the sampling upper-limit time At, the operation part determines B/At[Hz] as the input frequency measurement result by using the sampling number B measured in the sampling upper-limit time. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention receives a measurement value signal converted into a pulse frequency signal, calculates a pulse frequency from an average period of a predetermined number of sampling pulses, converts it to an analog output, and displays a pulse frequency on a display The present invention relates to a measurement method and apparatus using signals.

  4A and 4B are diagrams illustrating a conventional general measuring apparatus applied to a flow meter. FIG. 4A illustrates a schematic configuration thereof, and FIG. 4B illustrates a transmitted pulse frequency signal. The general measurement device shown in the figure usually receives a sensor and a sensor detection signal shaping unit, and a measurement value signal calculated by the sensor detection signal shaping unit, and converts it into an analog output or displays it on a display. And a flow rate measuring unit. The sensor detection signal shaping unit has a waveform shaping filter and a microprocessor (CPU), calculates the flow value based on the voltage or current signal detected by the sensor, and converts it to the number of pulses per pulse (pulse frequency). Output as a pulse frequency signal. The flow rate measurement unit that has received the pulse frequency signal has a microprocessor (CPU), and by counting the number of pulses per unit time of the pulse, the pulse frequency can be calculated to obtain an instantaneous flow rate value, Also, the total amount of flow can be obtained by integrating the number of pulses.

  The pulse time measurement in the flow rate measurement unit is usually performed by using a (timer) interrupt of a microprocessor (see Patent Document 1). As a result, as shown in FIG. 4B, the time measurement result becomes an integral multiple of the minimum resolution as the clock period. Thus, the measurement accuracy of each period of the pulse signal is determined by the minimum resolution. Therefore, when the measurement resolution is constant, the measurement accuracy increases as the measurement target time increases.

  In reality, considering the case where there is a variation in the pulse frequency input to the CPU, measure a plurality of pulse periods (time) and take the average to reduce the variation and increase the measurement accuracy. It has been done conventionally.

  Such a problem in the prior art will be described with reference to FIG. 5 as an example in which the number of samplings (number of pulse periods) is 4 pulses. FIG. 5A illustrates a pulse frequency signal, and FIG. 5B is a graph showing measurement results according to the prior art. In the flow rate measurement unit, as the number of sampling pulses is increased and the number of cycles to be averaged is increased, the measurement accuracy can be improved. It becomes difficult.

  It is assumed that t [sec] is measured as a period measurement value as the total time of the sampling number A (in the example, 4 pulses). In this case, the input frequency measurement result = A / t [Hz]. However, as the flow rate value decreases, the total time of the sampling number A increases. However, in practice, time measurement cannot be performed infinitely, so in the prior art, even if a predetermined time (sampling upper limit time) has passed, When A pulses were not input, measurement was stopped and the input frequency measurement result was set to 0 [Hz]. For example, when the sampling upper limit time At = 5 [sec] and the number of samplings A = 4, an input less than 1 / (At / A) = 1 / (5/4) = 0.8 [Hz] is shown in FIG. ), It was determined that “instantaneous flow rate = 0”. The dotted line in FIG. 5 (B) indicates the actual instantaneous flow rate that should be measured originally. Note that the minimum measurement frequency can be extended by reducing the sampling number A. However, in this case, the measurement accuracy is lowered.

The above-described prior art system is usually realized by microprocessor software, but such a system may be used in place of a conventional F / I (or F / V) conversion method. This F / I (or F / V) conversion method is a method of converting a pulse frequency signal into a current signal or a voltage signal in an analog manner by a hardware configuration, and was able to output almost linearly from 0 flow rate. . Therefore, when the above-described system is used instead of the F / I conversion method and the measurement result is output as an analog output, there is a problem that the compatibility in the small flow rate region is poor. For example, when the system is used where control is performed to stop the valve when the flow rate becomes 0, the above system determines that “instantaneous flow rate = 0” even though a small flow rate actually flows. As a result, the valve is closed despite a small flow rate. This is clearly inconvenient.
JP 2004-93467 A

  The present invention solves the above-mentioned problem that small measurement values cannot be measured in a method of measuring a plurality of pulse periods (time) in a measurement unit and increasing the measurement accuracy by taking an average thereof, The purpose is to make small measurements possible.

  Accordingly, an object of the present invention is to make it compatible with a conventional F / I conversion method in which a measurement value 0 is output almost linearly.

  The measuring method and apparatus using the pulse frequency signal of the present invention receives a pulse frequency signal corresponding to the signal detected by the sensor, calculates a pulse frequency from the average period of a predetermined number of sampling pulses, and outputs it as an analog output. And display on the display. A sampling upper limit time determination unit and an input frequency calculation unit are provided. When the predetermined sampling number A can be measured within the sampling upper limit time At, the input frequency calculation unit measures the total time t [sec] of the predetermined sampling number A, and the input frequency measurement result = A / t When the predetermined sampling number A cannot be measured within the sampling upper limit time At, the input frequency measurement result = B / At [ Hz].

  When the predetermined sampling number A cannot be measured within the sampling upper limit time At, the time t1 actually required for measuring the sampling number B is used, and the input frequency measurement result = B / t1 [Hz. ].

  In the present invention, in order to improve the measurement accuracy, if a set number of pulses cannot be sampled in a measurement method such as “sampling several pulses within a certain period of time”, the measurement is performed up to that point. The instantaneous flow rate is obtained from the number of pulses generated.

  In the present invention, naturally, within the guaranteed flow rate range, if the measurement is performed with guaranteed accuracy, if the flow rate falls below the guaranteed minimum flow rate, the flow rate does not become “0 flow rate”. As a result, when the measurement result is output as an analog output, the operation is similar to the conventional hardware F / I conversion output method, and this method can be replaced.

  Hereinafter, the present invention will be described based on examples. FIG. 1 is a diagram illustrating a case where a measuring device embodying the present invention is applied to flow measurement. The illustrated measuring apparatus includes a sensor and a sensor detection signal shaping unit, and a flow rate measurement unit that receives a measurement value signal calculated by the sensor detection signal shaping unit and converts the signal into an analog output or displays the analog output. It consists of. The sensor detection signal shaping unit can have the same configuration as that of the prior art described with reference to FIG. The sensor detection signal shaping unit has a waveform shaping filter, a microprocessor (CPU), etc., and converts the flow rate value into the number of pulses per pulse (pulse frequency) based on the voltage or current signal detected by the sensor. Output as a pulse signal.

  The downstream flow rate measurement unit that has received the pulse signal also has a microprocessor (CPU), and can obtain an instantaneous flow rate value by counting the number of pulses per unit time of the pulse. By integrating the number of pulses, the total amount of flow can be obtained.

  At this time, the exemplary flow rate measurement unit includes a sampling upper limit time determination unit, and, as long as it is within the upper limit time, the input frequency calculation unit, as in the related art, has a set total sampling time A. When t [sec] is measured as a periodic measurement value, the input frequency measurement result = A / t [Hz]. However, if the predetermined sampling number A cannot be measured within the upper limit time At, the input frequency measurement result = B / At [Hz] using the sampling number B measured within the upper limit time. When it is necessary to obtain a more accurate value, the input frequency measurement result = B / t1 [Hz] can be obtained by using the time t1 actually required for measuring the sampling number B.

  Further, the operation of the flow rate measuring unit will be described in detail using the flowchart shown in FIG. In step S1, the number of samplings A to be averaged and the sampling upper limit time At are set. In step S2, every time the rising edge of the input pulse is detected, the sampling number a counted from the reference reset pulse and the total time t [sec] from the rising edge of the reference pulse are measured (see FIG. 5A described above). )reference). In step S3, the measured sampling number a is compared with the set sampling number A. If a is not smaller than A, that is, if a is equal to A, the comparison result is No, and the process proceeds to step S4, where the input frequency measurement result = A / t [Hz]. Then, the process proceeds to step S8.

  If the comparison result is Yes and the number of measurements a has not reached the set number A, the process proceeds to step S5, where it is determined whether or not the measured total time t is less than or equal to the set upper limit time At. If it is less than or equal to the upper limit time At, the determination is yes and the process proceeds to step S2, and the sampling number a and the total time t are similarly measured for the next input pulse. When the measured total time t reaches or exceeds the set upper limit time At, the determination is no and the process proceeds to step S6. Here, the pulse number B measured within the upper limit time At is input. Then, in step S7, the input frequency measurement result = B / At [Hz] is set, the process proceeds to step S8, the measurement of this cycle is reset, and the measurement of the next cycle is started from step S2.

  Such an operation will be described with reference to FIG. 2 as an example where the sampling upper limit time At = 5 [sec] and the sampling number A = 4. The dotted line in FIG. 2 indicates the actual instantaneous flow rate that should be measured, and the solid line indicates the instantaneous flow rate measurement result. In this case, 1 / (At / A) = 1 / (5/4) = 0.8 [Hz] or more is measured in the same manner as in the prior art. The input less than this is conventionally determined as “instantaneous flow rate = 0”, but in the present invention, as shown by a solid line in FIG. 2, a staircase that approximates an actual instantaneous flow rate shown by a dotted line. It is expressed in the shape. In the above-described example, it is assumed that not the number of four sampling numbers A but three sampling numbers A can be detected within the sampling upper limit time At = 5 [sec]. In this case, it is determined that 1 / (At / A) = 1 / (5/3) = 0.6 [Hz]. Similarly, as the pulse frequency decreases, the detection state of only two pulses is reached through the detection state of two pulses within the sampling upper limit time At. In this state, it is determined that 1 / (5/1) = 0.2 [Hz]. Although a pulse frequency less than this is determined to be 0, in the present invention, a small flow rate up to a frequency corresponding to one pulse within the sampling upper limit time At can be measured with some errors.

It is a figure which illustrates the measuring device which materializes this invention. It is a figure explaining operation of a flow measurement part as an example when sampling upper limit time At = 5 [sec] and sampling number A = 4. It is a flowchart explaining operation | movement of a flow measurement part. It is a figure which illustrates the conventional general measuring device applied to the flowmeter, (A) is the schematic structure, (B) has illustrated the pulse frequency signal transmitted. It is a figure explaining the problem in a prior art as an example when the sampling number (pulse period number) is 4 pulses, (A) shows a pulse frequency signal, (B) exemplifies the measurement result by a prior art. ing.

Claims (4)

In the measurement method of receiving a measurement value signal converted into a pulse signal, calculating a pulse frequency from an average period of a predetermined number of sampling pulses, converting it to an analog output, and displaying it on a display,
When the predetermined sampling number A can be measured within the sampling upper limit time At, the total time t [sec] of the predetermined sampling number A is measured and obtained as input frequency measurement result = A / t [Hz]
When the predetermined sampling number A cannot be measured within the sampling upper limit time At, the input frequency measurement result = B / At [Hz] is obtained using the sampling number B measured within the sampling upper limit time. A measurement method using a pulse frequency signal. When the predetermined sampling number A cannot be measured within the sampling upper limit time At, using the time t1 actually required to measure the sampling number B, the input frequency measurement result = B / t1 [Hz] A measurement method using the pulse frequency signal according to claim 1 to be obtained. In a measurement device that receives a measurement value signal converted into a pulse signal, calculates a pulse frequency from an average period of a predetermined number of sampling pulses, converts it to an analog output, and displays it on a display device.
A sampling upper limit time determination unit and an input frequency calculation unit are provided,
When the predetermined sampling number A can be measured within the sampling upper limit time At, the input frequency calculation unit measures the total time t [sec] of the predetermined sampling number A, and the input frequency measurement result = A / Calculated as t [Hz]
When the predetermined sampling number A cannot be measured within the sampling upper limit time At, the input frequency measurement result = B / At [Hz] is obtained using the sampling number B measured within the sampling upper limit time. A measuring device using a pulse frequency signal. When the predetermined sampling number A cannot be measured within the sampling upper limit time At, using the time t1 actually required to measure the sampling number B, the input frequency measurement result = B / t1 [Hz] A measuring device using the pulse frequency signal according to claim 3 to be obtained.

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